1. Field of the Invention
The present invention relates to a bevel gear used in, for example, a differential gear of an automobile,, and more particularly, to a webbed bevel gear which is improved in mechanical strength by forming webs at the radial outer end of the bevel gear.
2. Description of the Related Art
In general, the strength of the gear is an important factor when considering to downsize a bevel gear, that is, downsizing a bevel gear box, or when also considering to use such a gear for machines with high-power engines.
The strength of the bevel gear is generally proportional to the size and cost of the gear. Accordingly, a current significant problem is how to obtain a bevel gear having a predetermined strength without requiring the enlargement of the gear.
In order to solve the above problem, as disclosed in Japanese Laid-Open Patent No. 63-215329, a webbed bevel gear has been developed in which the mechanical strength of the gear is improved by forming webs at the radial outer end of the gear. The bevel gear disclosed in the above Laid-Open patent was expected to be downsized and, at the same time, to improve the mechanical strength thereof.
Most of the damage arising in a gear results form the loss of a tooth due to bending or from pitting and scoring of the tooth surface. In order to avoid such damage, there have been many attempts to improve the strength of the tooth surface and the dedendum. If bending occurs at the dedendum, power fails to be transmitted so that the gear cannot function properly. In order to prevent such bending, with a view to mitigating the stress in the dedendum and to improving its strength, a webbed bevel gear having webs formed at the radial outer end of the gear has been put into practice.
However, such a conventional gear presents the following problems.
As an example of conventional gears which mitigate the stress in the dedendum, a webbed bevel gear generally denoted as 30 is shown in FIG. 7. Such a gear becomes heavier than conventional gears without webs, and also, the tooth bearing surface must be displaced inward in order to avoid interference with the mating gear. As a result, the transmission torque is decreased, and also, the load capacity is not increased as expected.
Also, in a bevel gear generally denoted as 32 provided with webs at the rear of the gear shown in FIG. 8, the dimensions thereof are increased and the gear box size is accordingly increased, thereby incurring an increase in the weight of differential gears.
Further, in a bevel gear generally denoted as 34 provided with webs to cover the addendum along the rear of the cone as shown in FIG. 9, the diameter of the gear must be increased in order to avoid interference with the mating gear, thereby incurring an increase in the weight of the gear as in the case of the previous gears described above.